The invention concerns structural panels and specifically relates to structural panels usable to construct vehicle bodies having no frames.
Many well known configurations are used for structural panels, one of the most common being a composite panel comprised of layers of different materials bonded together, such as wood sandwiched between sheets of metal to form doors of semi-trailers. Another common construction is a corrugated sheet bonded between two flat sheets in much the same way as cardboard for boxes. Still other configurations are known as "honeycomb" constructions due to their structural similarity to a bee's wax honeycomb. The honeycomb constructions for panels generally have adjoining tube-like cells with central axes normal to the general plane of the panel, the ends of the cells being bonded to opposed inner faces of the panel. It is also common for structural panels to be comprised of two or more layers of the same material bonded together, each layer having a different grain or fiber orientation, as, for example in plywood panels. Frequently, multiple corrugated sheets are bonded together with the corrugations of one or more sheets being normal to the corrugations in adjacent sheets.
Various problems have occurred with these well known constructions for panels. For example, composite panels tend to delaminate when they are bent, impacted or fatigued, the delamination being largely due to stress concentrations at bonding points. Such delamination is a limiting factor when using composite panels for supporting loads. Another, related problem with some known structural panels is inflexibility at bonding points between the outer sheets and the inner body of the panels, these panels often failing at the bonding points.
My invention overcomes the above problems by providing a structural panel that is formed of a single, unitary piece and not of several pieces fixed together by such means as adhesives, welding or rivets. My invention is a panel having two outer sheets and having at least one inner tray comprised of hollow apertured pyramids, the sheets and trays being cast together to form a single, continuous unit. The integration of the trays and sheets provides a stronger, more durable connection between outer sheets and inner panel structure than is accomplished with known structural panels. One embodiment of my invention may be regarded as two mutually perpendicular sets of corrugations occupying the same planar space between two outer sheets. This embodiment is more compact than the known multi-layer corrugated sheet wherein the corrugations in one layer are perpendicular to corrugations in an adjoining layer. My invention also avoids the delamination problems inherent in the conventional multi-layered construction.